Currently the use of plasma etching in the manufacture of integrated circuit devices is widespread. Typically the manufacture of integrated circuit devices involves the formation of multiple layers on the surface of a semiconductive wafer, typically of silicon. These layers need to be etched to desired patterns in accordance with desired device parameters. Typically, some of the etching needs to be anisotropic, for example in the creation of substantially vertical vias in the layers to provide conductive connections to particular regions of the semiconductive wafer, and some of the etching is preferably isotropic, for example in the planarization of surfaces of the layer-covered silicon wafer to facilitate the provision of the metalization layers used to provide interconnections between the components of the integrated circuit.
Because the apparatus used for such etching is expensive, it is generally important, for keeping costs adequately low, that the apparatus be capable of high throughput. To realize high throughput, it is important to keep the down-time of the apparatus short and its maintenance easy.
Apparatus designed particularly for isotropic etching has typically included a process chamber that includes a sleeve portion of relatively small diameter, a bell jar portion of relatively larger diameter, and a load-lock base where the workpiece being etched is supported, each usually of quartz or alumina. The top of the sleeve portion is generally provided with a capped opening through which the gaseous medium used for the etching is introduced into the process chamber. After introduction the gaseous medium flows down the sleeve portion past a pair of electrodes that are disposed outside the sleeve portion and between which is maintained a suitable radio frequency (r.f.) voltage. This voltage causes a capacitive discharge that ionizes the gaseous medium as it flows past and creates the desired plasma. To create the desired r.f. field conveniently, it is desirable that the electrodes be relatively close to one another. This necessitates that the sleeve portion have a relatively small diameter, typically of about three inches at the current state of the art. However, currently wafers to be etched typically have a diameter of eight inches and the trend is to even larger diameter wafers. Accordingly, the bell jar portion and the load-lock base, within which is housed a wafer to be etched, must have dimensions that accommodate the wafers. There is accordingly a significant change in the cross-section of the path of the gas as it leaves the sleeve portion and enters the bell jar portion.
To insure isotropic etching uniformly over the entire top surface of the wafer being etched, it is important that the plasma extend relatively uniformly across the top surface. To this end, it is the practice to include a "director" element in the sleeve portion below the capped opening. This director, which is typically a multipiece assembly that is bolted to the cap, provides a central opening through which the gaseous medium is introduced for flow initially vertically into the assembly. However, the flow is thereafter diverted radially by the director towards the inner wall of the sleeve portion for flow downwards past the electrodes that create the r.f. discharge into the bell jar portion to keep the high velocity jet of the process gas from interfering with the uniformity of the plasma.
Additionally, this director, which is typically of a dielectric such as quartz or alumina, serves usefully also to isolate the cap through which the gaseous medium is introduced from the plasma.
A problem that has arisen with the use of particular gaseous media that have been found desirable for use in isotropic etching, such as media that are oxygen-rich, is the deterioration of the screws that are used to fasten the director to the cap. The materials that are convenient to use for such screws, such as vespel, tend to erode in use. This results both in undesirably high particulate matter in the bell jar and in a sufficient weakening of the screws with time that the director is not maintained securely in place. The present invention provides a solution to this problem.